Image forming apparatus

ABSTRACT

The present invention provides a paper feed portion for image forming apparatuses having a simple structure capable of generating a carrying force and of preventing double feeding effectively. A paper feed roller  1  and a carrying auxiliary portion  2  are arranged in a symmetrical manner with respect to the paper feed path, that is, above the paper feed path on the upstream side and below the paper feed path on the downstream side respectively. In the carrying auxiliary portion  2 , a carrying force generating rib  22  is arranged at the center in the width direction and in a position facing the contact member  10   a  of the paper feed roller  1 , while double feed preventing ribs  23   a  and  23   b  are arranged in a symmetrical manner with respect to the carrying force generating rib  22  in the width direction. The upper surfaces  231   a  and  231   b  of the paper carrying upstream side end portions of the double feed preventing ribs  23   a  and  23   b  are positioned lower than the upper surface  221  of the paper carrying upstream side end portion of the carrying force generating rib  22 , and the upper end  233  of the wall surfaces of the paper carrying upstream side end portions of the double feed preventing ribs  23   a  and  23   b  is positioned on the paper carrying upstream side of the upper end  223  of the wall surface of the paper carrying upstream side end portion of the carrying force generating rib  22.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus in which paper placed on a paper feed tray is fed into the main body to form an image thereon, and more particularly to a structure of a paper feed portion for such an image forming apparatus.

2. Description of the Prior Art

Conventionally, in an image forming apparatus such as a dye-sublimation printer, sheets of paper having a predetermined shape and placed on a paper feed tray are fed into the main body one by one to form an image thereon. In this case, it is necessary to feed only one sheet of paper from a stack of paper placed on the paper feed tray.

As shown in FIG. 5, in a conventional image forming apparatus are therefore provided a paper feed roller for feeding paper and carrying force generating ribs arranged on the other side of the paper feed roller across the paper feed path to apply a predetermined carrying force to paper.

FIG. 5 is a view showing a paper feed portion of a conventional image forming apparatus, where FIGS. 5 (a), (b) and (c) are, respectively, a plan view, a side elevational view, and a partial perspective view of the paper carrying surface.

As shown in FIG. 5, the conventional paper feed portion comprises a paper feed roller 1 with the axis being perpendicular to the paper feed direction as well as horizontal to the ground and a carrying auxiliary portion 2 with carrying force generating ribs 20 a and 20 b provided thereon which is positioned on the paper carrying downstream side of and below the paper feed roller 1. The conventional paper feed portion then applies a carrying force to paper between the carrying force generating ribs 20 a and 20 b and the contact members 10 a and 10 b on the paper feed roller 1. This allows the paper to be fed in a predetermined direction (indicated by the thick arrow in FIG. 5). In this case, the height of the carrying force generating ribs 20 a and 20 b is preset to generate a predetermined carrying force and also to prevent double feeding (sheets of paper from being carried in an overlapped manner).

Also, as a structure for generating a predetermined carrying force for paper and for preventing double feeding is disclosed a paper feeding apparatus comprising a placing table with a recessed portion fitted to the shape of a paper feed roller formed therein (refer to Japanese Patent Laid-Open Publication No. Hei 7-126029 for example).

It is however difficult to set optimum conditions for generating a predetermined carrying force and for preventing double feeding in a paper feed portion of a conventional image forming apparatus having such a structure. That is, increasing the carrying force makes double feeding more likely, while the structure for preventing double feeding leads to a shortage of carrying force.

Although there exists an apparatus in which the height of ribs can be varied to obtain optimum conditions for the generation of a carrying force and for the prevention of double feeding, it has a complex structure, resulting in an increase in cost.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an image forming apparatus having a simple structure capable of generating a required carrying force and of preventing double feeding effectively.

The present invention is directed to an image forming apparatus for forming an image on paper fed by paper feed means, wherein the paper feed means comprises: a paper feed roller consisting of a contact member to be brought into contact with paper while being rotated and an axis member for transferring torque to the contact member; a carrying force generating rib arranged on the other side of the paper feed roller across the paper feed path to apply a carrying force to paper together with the paper feed roller; and a double feed preventing rib arranged on the other side of the paper feed roller across the paper feed path and in a position not facing the contact member to prevent double feeding of paper. The apparatus is then characterized in that the height of the paper carrying upstream side end portion of the double feed preventing rib is lower than that of the paper carrying upstream side end portion of the carrying force generating rib, that the wall surface of the paper carrying upstream side end portion of the double feed preventing rib has an inclination greater than that of the wall surface of the paper carrying upstream side end portion of the carrying force generating rib, and that the upper end of the wall surface of the paper carrying upstream side end portion of the double feed preventing rib is arranged on the paper carrying upstream side of the upper end of the wall surface of the paper carrying upstream side end portion of the carrying force generating rib.

With the arrangement above, the paper feed roller and the carrying force generating rib apply a carrying force to paper in a predetermined direction. In this case, the carrying force is set by the clearance between the paper feed roller and the wall surface of the paper carrying upstream side end portion of the carrying force generating rib as well as the upper end thereof. Then, thus set carrying force feeds (carries) paper, where multiple sheets of paper may be carried due to friction between them. Here, with the arrangement that the wall surface of the double feed preventing rib has an inclination greater than that of the wall surface of the carrying force generating rib and that the upper end of the wall surface of the double feed preventing rib is arranged on the paper carrying upstream side of the upper end of the wall surface of the carrying force generating rib, sheets of paper forced on by paper to be carried are to be separated from the paper at the wall surface of the paper carrying upstream side end portion of the double feed preventing rib as well as the upper end thereof.

The image forming apparatus according to the present invention is also characterized in that the carrying force generating rib is arranged at approximately the center in the direction perpendicular to the paper feed direction in the paper surface, and that a plurality of double feed preventing ribs are arranged in a symmetrical manner with respect to the carrying force generating rib in the direction perpendicular to the paper feed direction in the paper surface.

With the arrangement above, since a carrying force is to be applied to paper at the center in the direction perpendicular to the paper feed direction in the paper surface, the paper cannot be carried while being misaligned by a predetermined angle from the carrying direction and double feeding can be prevented at the symmetrical position with respect to the center position, whereby the paper carrying downstream side end face of sheets of paper separated is to be made perpendicular to the paper feed direction to prevent misalignment in the subsequent carrying operation.

The image forming apparatus according to the present invention is further characterized in that the wall surface of the paper carrying upstream side end portion of the double feed preventing rib has an arc shape recessed toward the rib main body.

With the arrangement above, since the wall surface of the paper carrying upstream side end portion of the double feed preventing rib has an arc shape recessed toward the main body, sheets of paper separated are to be brought into contact with the arc face to be put back to the initially placed position easily.

In accordance with the present invention, it is possible to construct an image forming apparatus having a simple structure capable of generating a predetermined carrying force and of preventing double feeding reliably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective outside view showing the schematic configuration of a paper feed portion of an image forming apparatus according to an embodiment of the present invention;

FIG. 2 is a plan view, a cross-sectional view along the line A-A and a cross-sectional view along the line B-B of the paper feed portion shown in FIG. 1;

FIG. 3 is a conceptual view showing the positional relationship between the carrying force generating rib and the double feed preventing ribs shown in FIGS. 1 and 2;

FIG. 4 is a conceptual view showing the paper feed operation of the paper feed portion of the image forming apparatus according to the present embodiment; and

FIG. 5 is a plan view, a side elevational view, and a partial perspective view of a paper feed portion of a conventional image forming apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Here will be described a paper feed portion of an image forming apparatus according to an embodiment of the present invention with reference to FIGS. 1 to 4.

FIG. 1 is a partial perspective view showing the configuration of the paper feed portion of the image forming apparatus according to the present embodiment. Also, FIGS. 2 (a), (b) and (c) are, respectively, a plan view, a cross-sectional view along the line A-A and a cross-sectional view along the line B-B of the paper feed portion shown in FIG. 1. Further, FIG. 3 is a conceptual view showing the positional relationship between the carrying force generating rib and the double feed preventing ribs shown in FIGS. 1 and 2.

The paper feed portion of the image forming apparatus according to the present invention comprises a paper feed roller 1 arranged above the paper feed path and a carrying auxiliary portion 2 arranged below the paper feed path.

The paper feed roller 1 consists of a rotation axis 10 c with the axis being perpendicular to the paper feed direction of the image forming apparatus in the paper surface, that is, parallel to the width direction of the image forming apparatus and a contact member 10 a having a predetermined length as well as a predetermined diameter greater than that of the rotation axis 10 c and arranged at approximately the center in the width direction. Then, on at least one end of the rotation axis 10 c is installed a drive unit (not shown in the figure) for rotating the rotation axis 10 c, the drive unit being adapted to drive the rotation axis 10 c to allow the entire paper feed roller 1 including the contact member 10 a to be rotated so that paper in contact with the contact member 10 a is carried in a predetermined direction (paper feed direction).

The carrying auxiliary portion 2 integrally comprises: a base body 21; a carrying force generating rib 22 arranged at approximately the center in the width direction of the base body 21; and two double feed preventing ribs 23 a and 23 b arranged in a symmetrical manner with respect to the carrying force generating rib 22 in the width direction. The carrying auxiliary portion 2 is then arranged below the paper feed path and in a position approximately symmetrical with the paper feed roller 1 across the paper feed path, and further placed in the main body (chassis) of the image forming apparatus not shown in the figure. In this case, the carrying auxiliary portion 2 is arranged on the paper carrying downstream side (indicated by the thick arrow in the figure) of the paper feed roller 1, and the upper end of the ribs 22, 23 a and 23 b is positioned higher than the lower end of the contact member 10 a of the paper feed roller 1.

The carrying force generating rib 22 comprises an approximately rectangular parallelepiped-shaped base material having a predetermined width in the width direction of the image forming apparatus as well as a predetermined length in the paper feed direction, and the paper feed roller 1 side end portion, that is, the paper carrying upstream side end portion thereof is formed higher than the other portions of the base material by a predetermined length. The wall surface 222 of the paper carrying upstream side end portion of the base material is formed inclined on the upper end side by a predetermined angle with respect to the lower part formed vertically. Also, the upper surface 221 of the paper carrying upstream side end portion is formed flat horizontally. Then, the carrying force generating rib 22 is arranged in such a manner that the center in the width direction of the carrying force generating rib 22 corresponds to that in the axial direction of the contact member 10 a of the foregoing paper feed roller 1.

The double feed preventing ribs 23 a and 23 b comprise a base material having approximately the same shape as the carrying force generating rib 22, and the paper carrying upstream side end portion thereof is formed higher than the other portions of the base material by a predetermined length, as is the case with the carrying force generating rib 22. The wall surfaces 232 a and 232 b of the paper carrying upstream side end portions of the base material are formed inclined on the upper end side by a predetermined angle with respect to the lower part formed vertically, and also in an arc shape recessed toward the base material. Also, the upper surfaces 231 a and 231 b of the paper carrying upstream side end portions are formed flat horizontally, and the upper surfaces 231 a and 231 b of the two double feed preventing ribs 23 a and 23 b are arranged at the same height. Then, the upper surfaces 231 a and 231 b of the double feed preventing ribs 23 a and 23 b are positioned lower than the upper surface 221 of the carrying force generating rib 22. In addition, the double feed preventing ribs 23 a and 23 b are arranged in a symmetrical manner with respect to the length (longitudinal) direction of the carrying force generating rib 22 as a symmetrical baseline in the width direction of the image forming apparatus.

Also, the upper end 233 of the wall surfaces 232 a and 232 b of the double feed preventing ribs 23 a and 23 b is arranged on the paper carrying upstream side of the upper end 223 of the wall surface 222 of the carrying force generating rib 22, and the inclination of the wall surfaces 232 a and 232 b of the double feed preventing ribs 23 a and 23 b is greater than that of the wall surface 222 of the carrying force generating rib 22.

The paper feed portion of thus arranged image forming apparatus feeds paper in accordance with the operation to be described hereinafter.

FIG. 4 is a conceptual view showing the paper feed operation of the paper feed portion of the image forming apparatus according to the present embodiment, where the state changes from (a) to (c) in order.

First, at the start of printing operation, that is, paper feed operation, the contact member 10 a of the paper feed roller 1 is brought into contact with the top paper 501 among a group of multiple sheets of paper 500 placed on a paper placing table 3 as shown in FIG. 4 (a). At the same time, the paper feed roller 1 rotates in such a manner as to carry the paper 501 toward the carrying force generating rib 22 and the double feed preventing ribs 23 a and 23 b. Here, the contact member 10 a of the paper feed roller 1 is made of a material that generates a predetermined friction against the paper 501, and therefore the rotation of the paper feed roller 1 (contact member 10 a) causes the paper 501 to be carried toward the ribs 22, 23 a and 23 b, that is, in the paper carrying downstream direction. In this case, since the paper 501 also has a predetermined friction against the paper 502, the carrying of the paper 501 causes the paper 502 to be carried in the same direction accordingly.

Next, as the rotation of the paper feed roller 1 continues, the paper 501 is carried in accordance with the amount of the rotation, and the leading end thereof is brought into contact with the wall surface 222 on the paper carrying upstream side in the carrying force generating rib 22 and the wall surfaces 232 (232 a and 232 b) on the paper carrying upstream side in the double feed preventing ribs 23 a and 23 b to be carried along the wall surfaces 222, 232 a and 232 b. In this case, since the paper 501, which is in direct contact with the contact member 10 a of the paper feed roller 1, is provided with a predetermined amount of carrying force from the contact member 10 a and the carrying force generating rib 22, the paper 501 is to be carried continuously in the paper carrying downstream direction without any effect thereon even when brought into contact with the upper end 233 of the wall surfaces 232 a and 232 b on the paper carrying upstream side in the double feed preventing ribs 23 a and 23 b, as shown in FIG. 4 (b). Meanwhile, the carrying downstream side leading end of the paper 502, which is in no direct contact with the contact member 10 a of the paper feed roller 1, runs head-on into the contact regions between the upper end 233 of the wall surfaces 232 of the double feed preventing ribs 23 a and 23 b, which exist on the paper carrying upstream side of the wall surface 222 of the carrying force generating rib 22, and the reverse side of the paper 501 (in no contact with the contact member 10 a of the paper feed roller 1). In this case, since the wall surfaces 232 a and 232 b on the paper carrying upstream side in the double feed preventing ribs 23 a and 23 b have a greater inclination, these wall surfaces function as a stopper for preventing the carrying of the paper 502. Therefore, the paper 502 cannot be carried toward the paper carrying downstream side over the point.

Then, even when the paper 501 is further carried in the paper carrying downstream direction, the leading end of the paper 502 runs head-on into the arc-shaped wall surfaces 232 and thereby falls into the position where it has been at the start of paper feeding, as shown in FIG. 4 (c).

With the arrangement above, it is possible to achieve a paper feed portion having a simple structure capable of generating a predetermined carrying force and of preventing double feeding.

Next will be described an image forming apparatus comprising such a paper feed portion. It is noted that the following descriptions are based on a dye-sublimation printer as an example of such an image forming apparatus.

The dye-sublimation printer is for printing color images, in which an ink ribbon is tightly stretched across a thermal head, the ink ribbon being adapted to be sent from the paper feed side and then reeled at the paper discharge side. Also, the ink ribbon is a connection of ink ribbons of cyan, magenta and yellow in this order. The length of each color ink ribbon is the same as the carrying direction length of paper on which a color image is to be printed.

When a color image to be printed is input to the dye-sublimation printer, color separation is made for the input color image to generate cyan, magenta, and yellow images. In the dye-sublimation printer, such a paper feed portion as mentioned above feeds paper 501 from a paper placing table (paper feed tray) 3 with a stack (multiple sheets) of paper 500 placed thereon into between the platen roller and the thermal head with the leading end of the cyan ink ribbon being aligned with that of the paper 501 just before the thermal head. When the leading end of the paper 501 reaches the printing position by the thermal head, the printing press lever is rotated to press the thermal head toward the platen roller with a sufficient pressing force. The paper 501 is to be carried using a paper carrying mechanism while keeping this state, where the ink ribbon and the paper 501 are overlapped with each other between the thermal head and the platen roller. Then, the paper carrying mechanism carries the paper 501 continuously, and the ink ribbon is reeled at the paper discharge side. When the rear end of the paper 501 reaches the printing position by the thermal head, the carrying of the paper 501 and the reeling of the ink ribbon are stopped, and the press lever is rotated to release the pressing force applied from the thermal head to the platen roller. Thus, the printing of a cyan image is completed to subsequently start the step of printing a magenta image over the cyan image.

In the state above, only the paper 501 is put back toward the paper feed side by the paper carrying mechanism, and fed into between the platen roller and the thermal head with the leading end of the magenta ink ribbon being aligned with that of the paper 501. When the leading end of the paper 501 reaches the printing position by the thermal head, the printing press lever is rotated to press the thermal head toward the platen roller with a sufficient pressing force. The paper 501 is to be carried using the paper carrying mechanism while keeping this state, where the ink ribbon and the paper 501 are overlapped with each other between the thermal head and the platen roller. Then, the paper carrying mechanism carries the paper 501 continuously, and the ink ribbon is reeled at the paper discharge side. When the rear end of the paper 501 reaches the printing position by the thermal head, the carrying of the paper 501 and the reeling of the ink ribbon are stopped, and the press lever is rotated to release the pressing force applied from the thermal head to the platen roller. Thus, the printing of a magenta image is completed to subsequently start the step of printing a yellow image over the magenta image.

Next, as is the case in the step of printing the foregoing magenta image, only the paper 501 is put back toward the paper feed side by the paper carrying mechanism, and fed into between the platen roller and the thermal head with the leading end of the yellow ink ribbon being aligned with that of the paper 501. When the leading end of the paper 501 reaches the printing position by the thermal head, the printing press lever is rotated to press the thermal head toward the platen roller with a sufficient pressing force. The paper 501 is to be carried using the paper carrying mechanism while keeping this state, where the ink ribbon and the paper 501 are overlapped with each other between the thermal head and the platen roller. Then, the paper carrying mechanism carries the paper 501 continuously, and the ink ribbon is reeled at the paper discharge side. When the rear end of the paper 501 reaches the printing position by the thermal head, the carrying of the paper 501 and the reeling of the ink ribbon are stopped, and the press lever is rotated to release the pressing force applied from the thermal head to the platen roller. Thus, the printing of a yellow image and therefore a color image is completed.

Applying such a paper feed portion as mentioned above to thus arranged image forming apparatus allows paper to be fed properly without double feeding, whereby it is possible to construct an image forming apparatus having a simple structure capable of preventing defective paper feeding and of reducing defective printing due to double feeding. 

1. An image forming apparatus for forming an image on paper fed by paper feed means, wherein said paper feed means comprises: a paper feed roller consisting of a contact member to be brought into contact with paper while being rotated and an axis member for transferring torque to said contact member; a carrying force generating rib arranged on the other side of said paper feed roller across the paper feed path and at approximately the center in the direction perpendicular to the paper feed direction in the paper surface to apply a carrying force to paper together with said paper feed roller; and a plurality of double feed preventing ribs arranged on the other side of said paper feed roller across the paper feed path and in positions not facing said contact member in a symmetrical manner with respect to said carrying force generating rib in the direction perpendicular to the paper feed direction in the paper surface to prevent double feeding of paper, in which the wall surfaces of the paper carrying upstream side end portions have an arc shape recessed toward the rib main body, the height of the paper carrying upstream side end portions of said double feed preventing ribs being lower than that of the paper carrying upstream side end portion of said carrying force generating rib, the wall surfaces of the paper carrying upstream side end portions of said double feed preventing ribs having an inclination greater than that of the wall surface of the paper carrying upstream side end portion of said carrying force generating rib, and the upper end of the wall surfaces of the paper carrying upstream side end portions of said double feed preventing ribs being arranged on the paper carrying upstream side of the upper end of the wall surface of the paper carrying upstream side end portion of said carrying force generating rib.
 2. An image forming apparatus for forming an image on paper fed by paper feed means, wherein said paper feed means comprises: a paper feed roller consisting of a contact member to be brought into contact with paper while being rotated and an axis member for transferring torque to said contact member; a carrying force generating rib arranged on the other side of said paper feed roller across the paper feed path to apply a carrying force to paper together with said paper feed roller; and a double feed preventing rib arranged on the other side of said paper feed roller across the paper feed path and in a position not facing said contact member to prevent double feeding of paper, the height of the paper carrying upstream side end portion of said double feed preventing rib being lower than that of the paper carrying upstream side end portion of said carrying force generating rib, the wall surface of the paper carrying upstream side end portion of said double feed preventing rib having an inclination greater than that of the wall surface of the paper carrying upstream side end portion of said carrying force generating rib, and the upper end of the wall surface of the paper carrying upstream side end portion of said double feed preventing rib being arranged on the paper carrying upstream side of the upper end of the wall surface of the paper carrying upstream side end portion of said carrying force generating rib.
 3. The image forming apparatus according to claim 2, wherein said carrying force generating rib is arranged at approximately the center in the direction perpendicular to the paper feed direction in the paper surface, and wherein a plurality of said double feed preventing ribs are arranged in a symmetrical manner with respect to said carrying force generating rib in the direction perpendicular to the paper feed direction in the paper surface.
 4. The image forming apparatus according to claim 3, wherein the wall surface of the paper carrying upstream side end portion of said double feed preventing rib has an arc shape recessed toward the rib main body.
 5. The image forming apparatus according to claim 2, wherein the wall surface of the paper carrying upstream side end portion of said double feed preventing rib has an arc shape recessed toward the rib main body. 